1. Field of the Invention
This invention relates to an apparatus for administering parenteral solutions to medical patients. In particular, this application is directed to an improved apparatus for delivering precise volumes of solutions at precise rates from more than one solution source.
2. Description of the Prior Art
Infusion delivery systems for delivering liquid to a patient from more than one solution source have been previously known. The most common systems use gravity flow and manually adjustable tubing clamps or pinch valves. They may employ a variety fo valves and junctions to control flow at the desired rate and sequence. Examples of such systems are described in U.S. Pat. Nos. 3,886,937; 4,034,754; 4,114,617; 4,219,022; 4,223,695; 4,236,515; 4,237,879; 4,237,880; 4,250,879; 4,252,116; 4,256,104; 4,256,105; and 4,258,712. Dual delivery systems relying on electronic flow control means are described in U.S. Pat. No. 4,094,318, for example.
Automatic flow control systems relying on a drop counter which measures the frequency of drop fall through a drip chamber have been previously known. In general, a light beam from a lamp to a light detector is positioned so that it is interrupted by drops falling through a drip chamber. The frequency of the breaking of the light beam and/or the time lapse between drops breaking the light beam are directly proportional to the flow rate and are used to determine adjustments to be made to a flow control valve to change flow to the desired rate. Examples of systems comprising drop counters and control systems responsive thereto are described in U.S. Pat. Nos. 3,163,179; 3,601,124; 3,886,937; 4,038,982; 4,314,567.
The prior art systems do not provide the precise control of the total delivered volume of small quantities of secondary solutions which can be obtained with the apparatus of this invention.